Compact multifrequency band antenna structure

ABSTRACT

A compact multifrequency band antenna structure is disclosed. Such antenna structure is comprised of a first and second antenna section, each one thereof arranged to form an integral antenna structure. The first antenna section is a slotted waveguide planar array antenna (designed for operation in one frequency band) which serves as the ground plane for the second antenna section (the latter section being designed for operation in a second frequency band). The second antenna section is constructed such that the polarization of the radiation associated therewith is orthogonal to the polarization of the radiation associated with the slotted waveguide planar array antenna, thereby increasing the electrical isolation of the two antenna sections. In disclosed embodiments the second antenna section is formed from stripline and microstrip and the radiating front face portion of the slotted waveguide planar array antenna forms a ground plane for such stripline and microstrip.

Nov. 6, 1973 COMPACT MULTIFREQUENCY BAND ANTENNA STRUCTURE Primary Examiner-Eli Lieberman Att0meyPhilip J. McFarland et al.

[57] ABSTRACT A compact multifrequency band antenna structure is disclosed. Such antenna structure is comprised of a first and second antenna section, each one thereof arranged to form an integral antenna structure. The first antenna section is a slotted waveguide planar array antenna (designed for operation in one frequency band) which serves as the ground plane for the second antenna section (the latter section being designed for operation in a second frequency band). The second antenna section is constructed such that the polarization of the radiation associated therewith is orthogonal to the polarization of the radiation associated with the slotted waveguide planar array antenna, thereby increasing the electrical isolation of the two antenna sections. In dis closed embodiments the second antenna section is formed from stripline and microstrip and the radiating front face portion of the slotted waveguide planar array antenna forms a ground plane for such stripline and microstrip.

3 Claims, 3 Drawing Figures BACKGROUND OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, a radio frequency antenna This invention relates generally to antenna structures 5 Str adap ed for Operation at X-band and L- and more particularly to compact antenna structures adapted to operate at more than one radio frequency band.

As is known in the art, it is sometimes desirable to have one compact antenna structure operate at more than one radio frequency band. For example, in a radar guided missile, a compact antenna carried by such missile and having, say, dual frequency adaptation could be used during two different modes of operation of the missile (i.e., for example, search/acquisition in C-band and track in X-band). Obviously in such an application space is at a premium within the missile and therefore it is highly desirable that any antenna structure occupy a minimum volume. Therefore, the use of two separate and independent antenna structures, each one thereof being adapted to operate at a different one of two frequency bands, would not be as desirable as one integral antenna structure with such adaptation because the latter structure is obviously more compact and occupies a smaller volume than the former structure.

SUMMARY OF THE INVENTION With this background of the invention in mind it is therefore an object of the invention to provide an improved, compact, integral, antenna structure adapted to operate over more than one radio frequency band.

This and other objects of the invention are attained generally by providing a first and a second antenna in an integral antenna structure. The first antenna is a slotted waveguide planar array antenna (designed for operation in one frequency band). The second antenna is a loop antenna (operative in a second frequency band) with the first antenna serving as its ground plane. The second antenna is fabricated such that the polarization of the radiation associated therewith is orthogonal to the polarization of the radiation associated with the slotted waveguide planar array antenna, thereby increasing the electrical isolation of the two antennas. In various embodiments of the invention the second 'antenna is formed from coaxial line, stripline and micro strip respectively. In the embodiments wherein the second antenna is formed from stripline or microstrip the radiating front face portion of the slotted waveguide planar array antenna serves as a ground plane for the stripline or microstrip.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as other objects, features and advantages thereof, may best be understood by reference to the following detailed description of illustrative embodiments, when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a sketch of a radio frequency antenna structure according to the principles of the invention;

FIG. 2 is a sketch of a portion of a radio frequency antenna structure according to the principles of the invention; and

FIG. 3 is a sketch of a portion of a radio frequency antenna structure, partially broken away, according to the principles of the invention.

band is shown to include a slotted waveguide planar array section 12 and having integral therewith a number of loop elements 14a 14d.

The slotted waveguide planar array section 12 is designed for operation at X-band. Such section 12 is therefore designed as a conventional slotted array antenna, here arranged in a conventional manner, for monopulse application such as that described in US. Pat. application Ser. No. 28,894 filedApr. 15, 1970 by W. Connerney, now US. Pat. No. 3,670,268 and assigned to the same assignee as the present application. Such section 12 may be viewed as being made up of a number, here eight, of rectangular waveguides. The bottom wide side 16a of each such waveguide forms the ground plane of the X-band antenna and the upper wide side thereof, 16b, has formed therein a number of rectangular slots in any conventional pattern. The upper wide side 16b therefore forms the radiating face of the Xband antenna. It is here noted that the polarization of the radiation associated with the X-band'antenna is orthogonal to the long dimensions of the rectangular slots (i.e., parallel to the arrow A).

An L-band loop antenna is formed by a number of loop elements, as loop elements 14a 14d, and the ground plane thereof is formed from the slotted waveguide planar array section 12. Each one of the loop elements 14a 14d is here made up of a conductor, here a brass rod l8a' 14d. Affixed to one end of the brass rod is a pin 20a 20d here also of brass which is coated with a dielectric 22a 22b and an outer conductor to form a coaxial cable. Such coaxial cable passes through a mounting block 24a 24d to conventional hybrid junctions (not shown) such hybrid junctions being arranged such that the L-band loop antenna is arranged for a monopulse application. That is, the RF energy associated with loop elements 14a 14d are summed to form the reference channel of the monopulse arrangement. The RF energy associated with loop elements l4a'and 14d is summed and subtracted from the RF energy associated with loopelement-l lc and'l4d to form a difference channel. The RF energy associated with loop elements 14a and 140 is summed and subtracted from the RF energy associated with the sum of RF energy associated with loop elements 14b and 14d.

Mounting blocks 24a 24d are made of suitable conductive metal and are affixed to the slotted waveguide planar array section hereby soldering in a conventional manner. The coaxial cable is supported within the mounting block by a press fit. The other end of the brass rod 18a -l8d has affixed thereto a strip of brass stock 26a 26d which is soldered to the brass rod. The brass stock is supported by the radiating face of the X- band antenna (i.e., waveguide planar array section) by a dielectric spacer/insulator28a 28d. The dielectric spacer/insulator is affixed to the radiating face of the X-band antenna in any conventional manner. The length of the loop elements 14a 14d are slected to provide for an electrically resonant L-band antenna.

antenna is along the path of current flow in each one of the loop elements (i.e., along the long dimension of the brass rod). Therefore, the polarization of the radiation associated with the X-band antenna and the L- band antenna are mutually orthogonal.

7 Referring now to FIGS. 2 and 3, the brass rods forming the loop elements 14a 14d of FIG 1 have been replaced by microstrip and stripline, respectively. In FIG. 3, portions of the upper ground plane of the stripline are cutaway from dielectric 30a so that the center conductor l8'c of such stripline is formed into a loop element, as shown. (The center conductor 18'c is disposed on a dielectric 32b.) The lower ground plane of the stripline is the radiating face 16b of slotted waveguide planar array section 12. In FIG. 2, as is known with microstrip, there is no requirement for an upper ground plane. The conductor 18"c is formed as a loop element as shown. Such conductor 18"c is disposed on a dielectric 32'. The lower ground plane of the microstrip is the radiating face 16b of the slotted waveguide planar array section 12.

Although preferred embodiments of the invention have been described in detail, it is to be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the appended claims.

What is claimed is:

l. A multifrequency band antenna structure comprising:

a. a slotted waveguide planar array antenna constructed for operation at a first frequency band and having a linear polarization; and,

b. a second antenna section formed integral with the slotted waveguide planar array antenna and having four loop antenna elements arranged for monopulse operation and constructed for operation at a second frequency band, the slotted waveguide planar array antenna serving as a ground plane for such second antenna section each one of such loop antenna elements having a linear polarization 0rthogonal to the polarization of the slotted waveguide planar array antenna.

2. The multifrequency band antenna recited in claim 1 wherein the elements of the second antenna section are formed from stripline and the ground plane of such stripline is the radiating face of the slotted waveguide planar array antenna.

3. The multifrequency band antenna recited in claim 1 wherein the elements of the second antenna section are formed from microstrip and the ground plane of such microstrip is the radiating face of the slotted waveguide planar array antenna. 

1. A multifrequency band antenna structure comprising: a. a slotted waveguide planar array antenna constructed for operation at a first frequency band and having a linear polarization; and, b. a second antenna section formed integral with the slotted waveguide planar array antenna and having four loop antenna elements arranged for monopulse operation and constructed for operation at a second frequency band, the slotted waveguide planar array antenna serving as a ground plane for such second antenna section each one of such loop antenna elements having a linear polarization orthogonal to the polarization of the slotted waveguide planar array antenna.
 2. The multifrequency band antenna recited in claim 1 wherein the elements of the second antenna section are formed from stripline and the ground plane of such stripline is the radiating face of the slotted waveguide planar array antenna.
 3. The multifrequency band antenna recited in claim 1 wherein the elements of the second antenna section are formed from microstrip and the ground plane of such microstrip is the radiating face of the slotted waveguide planar array antenna. 